M=6.4 earthquake strikes off the coast of Papua New Guinea

Today’s M=6.4 earthquake in Papua New Guinea struck near the island of New Ireland, in the eastern part of the country. (Photo from: Simon’s Jam Jar)

At 3:36 a.m. local time, a M=6.4 earthquake struck Papua New Guinea just off the island of New Ireland. The eastern part of the country is sparsely populated meaning people were only exposed to light and lesser degrees of shaking. Because of this damage and fatalities are unlikely, and so far no reports of them have come in. Another reason why strong shaking was not felt is because the earthquake occurred offshore and at a depth of 47 km, according to the USGS (The European-Mediterranean Seismological Centre assigned it a depth of 40 km). Based on the USGS focal mechanism, this earthquake was thrust in nature. While compressional earthquakes are common in this region, given the proximity to the New Britain Trench, the strike of today’s earthquake makes it hard to reconcile.

This Temblor map shows the location of today’s earthquake in Papua New Guinea. While this earthquake was compressional in nature, based on the quake’s strike, it was likely not associated with subduction at the New Britain Trench.

In the region around today’s earthquake, much of the seismicity is dominated by the subduction of the Australian Plate. North of the New Britain Trench, the Pacific Plate has been broken up into numerous microplates, all of which are being pushed in various directions. In the USGS map below, relative plate motions are shown, illustrating the complex dynamics of the region. Because of these plate motions, strike-slip and extensional earthquakes are also common. Nonetheless, large subduction zone earthquakes, including a M=7.9 in December 2016 are the events which cause the most damage and fatalities.

This map from the USGS shows historical seismicity and relative plate motions in the region around today’s M=6.4 earthquake (yellow star). What this map illustrates is that rapid deformation and high rates of seismicity is due to relative motion exceeding 100 mm/yr. In this map, one can see that the majority of quakes are associated with subduction at the New Britain Trench. (Map from USGS)

Based on the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, today’s earthquake should not be considered surprising. This model uses global strain rates and seismicity since 1977 to forecast the likely earthquake magnitude in your lifetime anywhere on earth. From this model, which is in the figure below, one can see that a M=7.75+ earthquake is likely in your lifetime in this area. Such a large magnitude is likely because the area is undergoing rapid deformation due to plate motions of upwards of 100 mm/yr. Should there be any large aftershocks (so far there is only one M=4.8 in our catalog) we will update this post.

This Temblor map shows the Global Earthquake Activity Rate (GEAR) model for the region around Papua New Guinea. This model uses global strain rates and seismicity since 1977 to forecast the likely earthquake magnitude in your lifetime anywhere on earth. From this model, one can see that today’s M=6.4 earthquake should not be considered surprising as a M=7.75+ quake is possible.